Electrically conductive ceramic sintered compact exhibiting low thermal expansion

ABSTRACT

An electroconductive low thermal expansion ceramic sintered body is disclosed which containing a β-eucryptite phase in a quantity of not less than 75 vol. % and not more than 99 vol. % and having an absolute value of thermal expansion coefficient of not more than 1.0×10 −7 /K at a temperature of 0° C. to 50° C., a volumetric specific resistance of not more than 1.0×10 7  Ω·cm, and a specific rigidity of not less than 40 GPa/g/cm 3 .

TECHNICAL FIELD

[0001] This invention relates to an electroconductive low thermalexpansion ceramic sintered body and specifically to a ceramic to be usedas the material for precision machine components.

BACKGROUND ART

[0002] In recent years, as the demand for higher precision in the fieldof precision processing technology has been mounting, it has beenbecoming important to warrant dimensional stability even for thematerials to be used for the members forming precision processingmachines. The materials for such members, therefore, have been becomingto require higher degrees of low thermal expansion property than everattainable. They further require high specific rigidity for the purposeof enabling these members to attain reduction in weight and addition toresonance frequency. For such uses as dictate high cleanliness in theenvironment of actual service, the materials are required to exhibitelectroconductivity sufficient for the purpose of preventing the membersmade thereof from being defiled by static electrification.

[0003] A review of the prior art from this point of view reveals theexistence of metallic low thermal expansion materials represented byInvar and Super Invar, low thermal expansion glass, and various lowthermal expansion ceramics such as cordierite, spodumene, and aluminumtitanate as low thermal expansion materials.

[0004] Though Super Invar is characterized by exhibiting a relativelylow thermal expansion coefficient of 1.3×10⁻⁷/K at ordinary roomtemperature and high electroconductivity, it is handicapped bypossessing marked low specific rigidity of less than 20 GPa/g/cm³ ascompared with ordinary ceramic materials. That is, the metallic lowthermal expansion materials are extremely disadvantageous in terms ofspecific rigidity because they suffer from high specific gravity andrelatively low Young's modulus as well.

[0005] Generally, ceramic materials are advantageous in terms ofspecific rigidity. As such a material, the low thermal expansion glasswhich has undergone a treatment for partial crystallization is disclosedin JP-A-50-132017 and in the catalog of Schott Corp. introducing itsproduct sold under the trademark designation of “Zerodur.” The ceramicmaterial which has undergone a treatment of partial crystallization,owing to the coexistence therein of a crystalline part and a vitreouspart having thermal expansion coefficients with different signs,realizes the low thermal expansion by counterbalancing the differentthermal expansions of the two parts throughout the whole of thematerial. The low thermal expansion glass of this quality, however, ishandicapped by lacking sufficient electroconductivity notwithstandingthe thermal expansion coefficient thereof is practically nil at roomtemperature. The specific rigidity thereof is about 35 GPa/g/cm³, amagnitude of which, though surpassing that of Super Invar, can hardly berated as satisfactory.

[0006] The so-called low thermal expansion ceramics such as cordierite,spodumene, and aluminum titanate exhibits neither necessarily highspecific rigidity nor fully sufficient electroconductivity.

[0007] In the technical field different from that of the presentinvention, the technique concerning the electroconductive low thermalexpansion material that is aimed at providing a heater material enjoyingexalted thermal shock properties has been in existence. The technique,however, is at a disadvantage in failing to impart fully satisfactorilylow thermal expansion to the produced material.

[0008] JP-B-53-47514 and JP-B-60-37561, for example, discloseelectroconductive low thermal expansion ceramics having anelectroconductive substance dispersed in substances of a negativethermal expansion coefficient or a very small positive thermal expansioncoefficient. The inventions of these publications are directed towardaccomplishing low thermal expansion by dispersing a compound possessinga positive thermal expansion coefficient in the matrix formed of acompound possessing a negative or very small positive thermal expansioncoefficient and thereby counterbalancing or lowering the mutual thermalexpansions throughout the whole of the material. In this respect, theseinventions have utilized the same technique disclosed in JP-A-50-132017mentioned above. The inventions of JP-B-53-47514 and JP-B-60-37561,however, are directed toward a technique which is characterized by usingas the compound to be dispersed in the matric phase a uniphaseelectroconductive substance and allowing at least part of this substanceto continue and form a network throughout the whole of the material andthereby securing electroconductivity of the entire material. Theseceramics, however, have failed, as demonstrated in examples cited inJP-B-53-47514, to realize satisfactorily low thermal expansivity becausethey require to disperse a large quantity of an electroconductive phaseand, therefore, the absolute values of their thermal expansioncoefficients are at least 4.2×10⁻⁷/K, a markedly large magnitude ascompared with the thermal expansion coefficient of Super Invar.

[0009] Generally, since an electroconductive substance has a largethermal expansion coefficient, a matrix containing an electroconductivephase in a large ratio cannot realize a low thermal expansion property.If this matrix conversely has a small electroconductive phase content,it will be unable to acquire satisfactory electroconductivity.JP-B-53-47514, for example, cites an example which demonstrates thedependency of specific resistance and thermal expansion coefficient onthe quantity of the electroconductive material incorporated in thematerial. The results of this example deny that such satisfactoryelectroconductivity and low thermal expansion properties are at presentsimultaneously fulfilled.

[0010] The technique which, as disclosed in JP-B-53-47514, secureselectroconductivity of the whole material by incorporating anelectroconductive phase in a matric phase which is an insulatingmaterial, causing at least part of the electroconductive phase to bedispersed in a continued state, and thereby forming a network of theelectroconductive phase throughout the whole of the material. Gurland'sreport (Gurland, J., 1966, Trans. Metals Soc. AIEM, vol. 236, 642) isavailable for referential use. According to this report, as demonstratedby an experiment in a Bakelite-silver particles system, when thequantity of the electroconductive substance is not less than about 30%by volume, the electroconductive substance dispersed in the insulatingmaterial attains thorough mutual contact enough to realizeelectroconductivity of the whole material. It is extremely difficult forthe reason stated above to realize a satisfactorily low thermalexpansion property with the quantity of the electroconductive substanceset in the neighborhood of this volumetric ratio. No case of succeedingin realizing this property has ever been reported to literature.

[0011] Even the invention of JP-B-60-37561, which utilizes a techniquesimilar to the technique of JP-B-53-47514, requires a substance of lowthermal expansion coefficient to incorporate therein not less than 25%by volume of an electroconductive phase and, consequently, fails torealize low thermal expansion in addition to securing satisfactoryelectroconductivity.

[0012] The addition of carbon black to a material of low thermalexpansion is possibly used, as mentioned in JP-A-11-343168, as a meansfor blackening the material with the object of imparting a sunproofingproperty. Though carbon black exhibits electroconductivity, the soleaddition of carbon in the quantity specified in the specification tocordierite does not result in acquiring such satisfactoryelectroconductivity as mentioned above.

[0013] The task which this invention aims to fulfill, therefore, residesin solving the problems confronting the prior art and providing amaterial of low thermal expansion which exhibits high specific rigidityand satisfactory electroconductivity as well with a view to realizingsuch precision machine members as demand a high degree of cleanlinessand enjoy light weight and high dimensional accuracy.

DISCLOSURE OF THE INVENTION

[0014] We have found that the task mentioned above is fulfilled by acomposite ceramic sintered body having carbon or a compound containingcarbon other than SiC, and TiN or SiC particles simultaneously dispersedin a β-eucryptite type ceramic capable of negative thermal expansion andfurther having a fine texture thereof optimized. They have consequentlyperfected this invention.

[0015] Specifically, this invention concerns a ceramic sintered bodycapable of high specific rigidity, electroconductivity, and low thermalexpansion, which is characterized by containing not less than 75% byvolume and not more than 99% by volume of a β-eucryptite phase andfilling the balance less the β-eucryptite phase with carbon or acompound containing carbon other than SiC (hereinafter abbreviated as“carbon compound”) and TiN or SiC particles, and having a thermalexpansion coefficient of the absolute value of not more than 1.0×10⁻⁷/Kat a temperature in the range of 0° C.-50° C., a volumetric specificresistance of not more than 1.0−10⁷ Ω·cm, and a specific rigidity of notless than 40 GPa/g/cm³. This sintered body contains 0.5-4% by volume ofa carbon compound and 0.5-12% by volume of TiN particles or 6-24.5% byvolume of SiC particles. It is characterized by the β-eucryptite phasehaving an average particle diameter in the range of 0.5-5 μm and the TiNparticles having an average particle diameter in the range of 0.5-3 μmor the SiC particles having an average particle diameter in the range of0.2-3 μm. Further, this electroconductive low thermal expansion ceramicsintered body has a textural structure in which the TiN or SiC particlesare discretely dispersed, further the carbon compound exists as a grainboundary phase in at least part of the β-eucryptite phase and/or thegrain boundary of the TiN particles or the SiC particles, and theaverage thickness of the grain boundary and the grain boundary phase inthe vertical direction is not more than 10% of the average crystalparticle diameter of the β-eucryptite.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] FIGURE depicts a typical fine structure of an electroconductivelow thermal expansion ceramic sintered body contemplated by thisinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0017] In the process for the production of a semiconductor, whichrequires a processing technique of the highest precision, it has beenbecoming essential for the positioning to be effected with highprecision of not more than 100 nm. For the purpose of improving thethroughput, the supporting member for a semiconductor producing devicemust be moved at a high speed to a place prescribed for the positioning.

[0018] The thermal expansion of any of the members of asemiconductor-producing device forms a major factor for the degradationof precision. When a member having a thermal expansion coefficient of10×10⁻⁷/K and measuring 500 mm in size is subjected to a change of 1° C.in its temperature, it gives rise to such a deviation as 500 nm in theterminal surface thereof. To preclude such an influence as this, theabsolute value of the thermal expansion coefficient of this member isrequired to be limited to not more than 1.0×10⁻⁷/K.

[0019] Further, the supporting member generates vibration in consequenceof the movement thereof at a high speed and this vibration forms afactor for lowering precision and reducing a throughput. From the pointof view of curbing this vibration, the member is required to exhibitgreater specific rigidity than the existing low thermal expansion glass.Particularly, this specific rigidity is required to be not less than 40GPa/g/cm³.

[0020] Further, the member is also required to possess satisfactoryelectroconductivity for the purpose of preventing the member from beingdefiled by electrization. The term “satisfactory electroconductivity” asused herein refers to such electroconductivity as realizes a volumetricspecific resistance of not more than 1.0×10⁷ Ω·cm.

[0021] The electroconductive low thermal expansion ceramic contemplatedby this invention contains mainly a β-eucryptite phase for the followingreason. The sintered body is required to have the matrix phase thereofformed of a compound of negative thermal expansion for the purpose ofobtaining a ceramic sintered body of low thermal expansion. As examplesof the compound mentioned above, β-eucryptite phase, aluminum titanate,spodumene, and cordierite may be cited. Only when the β-eucryptite,which exhibits a large negative thermal expansion among them, is usedfor the matric phase, such low thermal expansion property,electroconductivity, and specific rigidity as are aimed at can beattained.

[0022] The term “β-eucryptite phase” as used herein means a ceramic suchas a composition of this molar ratio,Li₂O:Al₂O₃:SiO₂=0.8-1.2:0.8-1.2:1.6-2.4.

[0023] The reason for selecting TiN or SiC as a dispersing substance isthat this substance is capable of heightening the specific rigidity of acomplex ceramic to be produced. Even when an electroconductivehigh-rigidity substance such as WC is utilized as the dispersionparticle, it is difficult to attain low thermal expansion and highspecific rigidity at the same time.

[0024] In order that the ceramic contemplated by this invention maysecure low thermal expansion property, electroconductivity, and highspecific rigidity all at once, it is required to contain TiN or SiCparticles and the carbon compound at the same time. If these twocomponents are contained independently, the expected propertiesmentioned above will not be attained even when the content of the TiN orSiC particles or the carbon compound falls in the specified range. Inthe preferred embodiment of the present invention, the sintered bodycontains 0.5-4% by volume of the carbon compound and 0.5-12% by volumeof the TiN particles or 6-24.5% by volume of the SiC particles. Thequantities in these ranges represent preferred contents of the relevantcomponents for the sake of realizing such thermal expansion coefficient,volumetric resistivity, and specific rigidity specified by thisinvention. Only by an adequate combination of the quantity of the carboncompound and the quantity of the TiN particles or the quantity of theSiC particles falling in the relevant ranges specified above, the targetphysical constants of this invention are attained. The absolute value ofthe thermal expansion coefficient of the sintered body exceeds1.0×10⁻⁷/K when the content of TiN particles falls short of 0.5% byvolume or exceeds 12% by volume or the content of SiC particles fallsshort of 6% by volume or exceeds 24.5% by volume. Thus, any deviation ofsuch content from the specified range is unfavorable. Particularly whenthe content of the TiN particles or the content of the SiC particlesfalls short of 0.5% by volume or 6% by volume respectively, the objectof this invention is not attained because the specific rigidity alsofalls short of 40 GPa/g/cm³. When the content of the carbon compound issmaller than 0.5% by volume, the thermal expansion coefficient is notaffected. When it is larger than 4% by volume, however, it becomesdifficult to attain the target low thermal expansion coefficient. Asregards the electroconductivity, no sufficient electroconductivity issecured when the content of the carbon compound and the content of TiNparticles or the content of SiC particles are smaller than therespectively prescribed quantities. Further, as regards the content ofthe carbon compound, if this content exceeds 4% by volume, the excesswill result in inhibiting the ceramic from being sintered, lowering theelastic modulus of the sintered body, and confining the specificrigidity below 40 GPa/g/cm³. The content exceeding 4% by volume,therefore, is unfavorable because it does not conform to the object ofthis invention.

[0025] The average crystal particle diameter of the β-eucryptite phaseought to assume a magnitude in the range of 0.5-5 μm and that of the TiNparticles and that of the SiC particles respectively a magnitude in therange of 0.5-3 μm and a magnitude in the range of 0.2-3 μm. When thesemagnitudes deviate from the respective ranges, satisfactoryelectroconductivity and low thermal expansion property cannot besimultaneously realized. It is necessary that the carbon compound bepresent as a grain boundary phase in the grain boundary of theβ-eucryptite phase and the TiN particles or the SiC particles and theaverage thickness of the grain boundary phase in the directionperpendicular to the grain boundary be not more than 10% of the averagecrystal particle diameter of the β-eucryptite. If the average thicknessexceeds this size, it will become impossible to obtain satisfactoryelectroconductivity.

[0026] FIGURE is a diagram portraying the typical fine texture of anelectroconductive low thermal expansion ceramic according to thisinvention. The fine texture is characterized by the fact that TiN or SiCparticles 3 are dispersed discretely therein and further the carboncompound 2 is present as a grain boundary phase in at least part of theβ-eucryptite phase 1 and/or the grain boundary of TiN or SiC particles3. The preceding expression that the particles are discretely dispersedin the fine texture describes the fact that TiN or SiC particles 3 arenot mutually contacting to form a chain-like network. The statement thatthe carbon compound 2 is present in the β-eucryptite phase 1 and in thegrain boundary of the TiN or SiC particles 3 describes the fact that thecarbon compound is present with a certain thickness in the grainboundary. This thickness relative to the direction perpendicular to thecrystal grain boundary of the β-eucryptite is preferred to be not morethan 10% of the average crystal particle diameter of the β-eucryptite.The statement that the carbon compound is present with a certainthickness in the grain boundary describes the fact that the carboncompound is present contiguously in the form of independent particles tothe β-eucryptite phase and the grain boundary of the TiN or SiCparticles or the fact that the carbon compound is in such a situation asentrains segregation of carbon in the neighborhood of grain boundary ofcrystal particles having an average particle diameter. For the purposeof deciding the volumetric ratio of individual particles or a compoundin a given material, the method which determines this volumeric ratio bycutting the material in an arbitrary plane, measuring area radios of theindividual particles appearing in the cut plain, and performing anecessary calculation using the measured area ratios may be utilized.Otherwise, when the volumetric change occurring after the calcination isconsidered to be negligible, the volumetric ratio maybe found from theweight-mixing ratio of components of the raw material powder and thedensity of each of the components.

[0027] The novel point of the material contemplated by this inventionconsists in enabling the carbon compound to exist in the form of a thinlayer in the β-eucryptite phase and in the grain boundary of the TiN orSiC particles and secure electroconductivity despite the addition of anelectroconductive substance in such a small quantity, as has beenheretofore unattainable, by adding the carbon compound and the TiN orSiC particles together in the form of a composite and restricting boththe quantities thereof so added and the fine texture of the sinteredbody, and in realizing such high specific rigidity, as has never beenattained by the conventional low thermal expansion material, byselecting either TiN or SiC as the material for the dispersingparticles. That is, this invention makes it possible by utilizing thecarbon compound as an electroconductive grain boundary phase to securesufficient electroconductivity in spite of the presence of anelectroconductive phase in an extremely small quantity as compared withthe conventional countertype. Further, the presence of the TiN or SiCparticles having a specified particle diameter also contributes to therealization of the electroconductivity in consequence of the addition ofsuch particles in the quantity prescribed by this invention.Specifically, for the purpose of acquiring the electroconductivitysolely with the grain boundary phase of the carbon compound, thevolumetric ratio of the carbon compound would surpass markedly thequantity specified by this invention. The presence of the TiN or SiCparticles, however, enables the volumetric ratio of the carbon compoundto be effectively lowered.

[0028] The carbon compound is not particularly restricted on account ofthe sort of form but required to be such a substance as survives in theform of an electroconductive substance or varies during the course ofcalcining the ceramic. As examples of the carbon compound, carbon black,graphite, and titanium carbide may be preferably cited. Among them, thecarbon black proves particularly favorable.

[0029] According to this invention, by forming a low thermal expansionceramic comprising the β-eucryptite phase as a main component andfurther incorporating therein TiN particles or SiC particles and acarbon compound, it is possible to secure the electroconductivity inspite of the addition of an electroconductive substance in a markedlysmall quantity as compared with the prior art and thereby realize amaterial of such high specific rigidity, electroconductivity, and lowthermal expansion as have never been attained heretofore.

[0030] The ceramic sintered body contemplated by this invention has acomposition comprising the β-eucryptite mainly and is formed by theordinary powder sintering. With the object of attaining compaction ofthe texture more effectively, such a sintering method as hot press orhot isostatic press may be utilized. Here, the carbon compound and theTiN particles or the SiC particles must exist in the forms mentionedabove in the fine texture of the ceramic sintered body.

[0031] To manufacture the ceramic described above, first lithium oxide,aluminum oxide, and silicon oxide are weighed out in such quantities asform a eucryptite composition and further a TiN powder or a SiC powderand a carbon compound are weighed out in prescribed quantities and theyare mixed together in a ball mill to produce a mixed powder. Here, thesources for lithium, aluminum, and silicon are not particularlyrestricted. Spodumene, petalite, lithium carbonate, etc. may be utilizedin a combination thereof. The known raw materials containing lithium,aluminum, and silicon may be suitably selected and used herein. Thecarbon compound to be used herein is not particularly restricted onaccount of factors such as form and origin. Carbon black and graphitemay be added. The residual carbon of the binder used in the raw materialpowder, the type of carbon addable during the course of process, and acompound containing carbon may be utilized. Among them, the carbon blackmay be particularly selected as an inexpensive and optimum raw material.

[0032] As the raw material, the TiN powder is preferred to have anaverage particle diameter in the range of 0.5-3 μm and the SiC powder anaverage particle diameter in the range of 0.2-3 μm. If the averageparticle diameter deviates from this range, it will become difficult torealize a low thermal expansion property and satisfactoryelectroconductivity at the same time. When the carbon source for thecarbon compound is secured by the use of an additive, the particlediameter of the raw material of this additive forms an important factor.This particle diameter must be as small as permissible. Particularlywhen the primary particle diameter is not more than 50 nm, especiallynot more than 20 nm, the material texture for the sintered body aimed atby this invention can be realized. If the primary particle diameter ofthe raw material for the carbon compound exceeds 0.5 μm, the excess willresult in rendering it difficult to obtain the satisfactoryelectroconductivity with stability. As means to determine the particlediameter of the raw material, known methods such as those which effectthe determination by means of a laser scattering or specific surfacearea may be utilized.

[0033] The mixed powder thus obtained is formed in a required shape by ameans such as a molding press and an isostatic press and then calcined.Otherwise, the powder may be placed in a die, pressed, and calcined asin the case of a hot press. Other known methods in popular use are alsoavailable. The formation is not limited to the methods cited above.

[0034] As respects the conditions for the calcination, the temperatureis not lower than 1000° C. and not higher than 1420° C., preferably notlower than 1250° C. and not higher than 1400° C. and the atmosphere isformed of oxygen of a concentration of not more than 1000 ppm andpreferably formed of an inert gas such as nitrogen or argon of aconcentration of not more than 100 ppm. If the temperature deviates fromthe range specified above, the deviation will result in preventing theβ-eucryptite phase from being formed with stability and rendering itimpossible to attain electroconductivity and a low thermal expansionproperty at the same time. The sintering resorting to the hot press orthe hot isostatic press proves advantageous for the purpose of attainingthe compaction more effectively. The pressure to be used by such a pressfor the compaction proves effective when it exceeds 10 MPa. Thecalcination temperature and the calcination atmosphere used for thecompaction are the same as those described above.

[0035] Now, this invention will be more specifically described belowwith reference to examples. This invention is not limited by suchillustrations.

EXAMPLES 1-5 AND COMPARATIVE EXAMPLES 1-6

[0036] In a ball mill, were mixed 24.3 parts by weight of lithiumcarbonate (average particle diameter 2.2 μm), 34.2 parts by weight ofaluminum oxide (average particle diameter 0.6 μm), and 41.5 parts byweight of silicon oxide (average particle diameter 0.8 μm). The powderconsequently formed was recovered and then calcined in the atmosphericair at 1300° C. The calcined powder and TiN particles of an averageprimary particle diameter of 3 μm and carbon black of an average primaryparticle diameter of 20 nm were added together, pulverized in a ballmill, and mixed till a mixed powder of satisfactorily uniformcomposition was formed. The mixed powder thus obtained was calcined witha hot press in the atmosphere of nitrogen at a temperature of 1320°C.-1370° C. under a pressure of 20 MPa. The quantities of the carbonblack and the TiN particles were so adjusted as to form a compositionindicated in Table 1 after calcination. The volumetric ratios shown inTable 1 were found from the observation of an image under a transmissionelectron microscope (TEM) and the EDX analysis. Comparative Example 6was performed by following the procedure described above, except thatgraphite having an average particle diameter of 2.1 μm was used insteadof carbon black.

[0037] The texture of the sintered body thus obtained was composed of aβ-eucryptite phase having an average crystal particle diameter of 0.5-5μm and TiN particles having an average particle diameter of 0.5-3 μm. Inthe experiments except for Comparative Examples 4 and 6, the EDXanalysis with a TEM detected inspissation of carbon in the form of agrain boundary phase in the grain boundary of at least part of theparticles mentioned above in the region of not more than 10% of theaverage crystal particle diameter of the β-eucryptite phase. There were,in Comparative Example 6, numerous carbon particles having particlediameters exceeding 1 μm in the sintered body. The properties of theproduced sintered bodies are shown in Table 1. It is clear from the dataof examples given in Table 1 that it was possible to satisfy the thermalexpansion coefficient, specific resistivity, and specific rigidity byconfining the composition of a sintered body within the range specifiedby this invention. In contrast, in Comparative Example 1, the expectedthermal expansion coefficient was not obtained because of unduly largequantity of TiN. In Comparative Example 2, the expected properties werealso not obtained at all because no TiN was added and the quantity ofthe carbon compound was unduly large. In Comparative Example 3, theabsolute value of thermal expansion coefficient was large and thespecific rigidity was low because the quantity of TiN was not sufficientand the quantity of the carbon compound was unduly large. In ComparativeExample 4, the properties other than the specific rigidity were notsatisfied because the quantity of TiN was unduly large and no carboncompounds were contained. In Comparative Example 5, the specificrigidity was markedly low and the absolute value of thermal expansioncoefficient failed to reach the target level because the quantity of thecarbon compound was unduly large. In Comparative Example 6, theproperties other than the absolute value of thermal expansioncoefficient were not satisfied because the fine texture of the sinteredbody specified by this invention was not realized. TABLE 1 PropertiesAbsolute value of Composition (vol. %) thermal expansion SpecificSpecific Carbon coefficient resistivity rigidity β-eucrytite TiNcompound (×10⁻⁷/K) (×10⁷Ω × cm) (GPa/g/cm³) Example 1 97.2 0.8 2 0.50.87 45 Example 2 97 2 1 0.1 0.56 47 Example 3 91 8 1 0.08 0.21 48Example 4 89 8 3 0.5 0.13 47 Example 5 87 10 3 0.8 0.062 49 Com. Example1 79 18 3 5.1 0.021 51 Com. Example 2 82 0 18 2.1 5.5 29 Com. Example 382.7 0.3 17 1.5 0.9 31 Com. Example 4 80 20 0 8.9 81 49 Com. Example 581 10 9 1.8 0.082 34 Com. Example 6 79 8 13 0.7 5.3 38

EXAMPLES 6-10 AND COMPARATIVE EXAMPLES 7-12

[0038] In a ball mill, were mixed 25.0 parts by weight of lithiumcarbonate (average particle diameter 2.2 μm), 34.4 parts by weight ofaluminum oxide (average particle diameter 0.6 μm), and 40.6 parts byweight of silicon oxide (average particle diameter 0.8 μm). The powderconsequently formed was recovered and then calcined in the atmosphericair at 1300° C. The calcined powder and SiC particles of an averageprimary particle diameter of 0.7 μm and carbon black of an averageprimary particle diameter of 20 nm were added together, and pulverizedin a ball mill to form a mixed powder of satisfactorily uniformcomposition. The mixed powder thus obtained was calcined in theatmosphere of nitrogen at a temperature of 1300° C.-1370° C. Thequantities of the carbon black and the SiC particles were so adjusted asto form a composition indicated in Table 2 after calcination. Thevolumetric ratios shown in Table 2 were found from the observation of animage under a TEM and the EDX analysis. Comparative Example 12 wasperformed by following the procedure described above, except thatgraphite having an average particle diameter of 2.1 μm was used insteadof carbon black.

[0039] The texture of the sintered body thus obtained was composed of aβ-eucryptite phase having an average crystal particle diameter of 0.5-5μm and SiC particles having an average particle diameter of 0.2-3 μm. Inthe experiments except for Comparative Examples 7-9 and 12, the EDXanalysis with a TEM detected inspissation of carbon in the form of agrain boundary phase in the grain boundary of at least part of theparticles mentioned above in the region of not more than 10% of theaverage crystal particle diameter of the β-eucryptite phase. InComparative Example 12, there were numerous carbon particles havingparticle diameters exceeding 1 μm in the sintered body. The propertiesof the produced sintered bodies are shown in Table 2. It is clear fromthe data of examples given in Table 2 that it was possible to satisfythe thermal expansion coefficient, specific resistivity, and specificrigidity by confining the composition of a sintered body within therange specified by this invention. In contrast, in Comparative Example7, the thermal expansion and the specific rigidity did not have expectedmagnitudes because of unduly small quantity of SiC. In ComparativeExample 8, the absolute value of thermal expansion coefficient waslarger than the target magnitude because of unduly large quantity ofSiC. In Comparative Example 9, the thermal expansion and the specificrigidity reached the target magnitudes. In Comparative Examples 7-9,however, the expected specific resistivity was not obtained invariablybecause no carbon compound was contained. In Comparative Example 10, theexpected properties were not obtained at all because no SiC was added.In Comparative Example 11, the absolute value of thermal expansioncoefficient was large and the specific rigidity was low because thequantity of SiC was not sufficient and the quantity of the carboncompound added was unduly large. In Comparative Example 12, the expectedspecific resistivity was not obtained because the fine texture of thesintered body specified by this invention was not realized. TABLE 2Properties Absolute value of Composition (vol. %) thermal expansionSpecific Specific β- Carbon coefficient resistivity rigidity eucryptiteSiC compound (×10⁻⁷/K) (×10⁷Ω × cm) (GPa/g/cm³) Example 6 88 8.5 3.5 0.70.87 51 Example 7 84 14.5 1.5 0.5 0.75 57 Example 8 82 16.7 1.3 0.3 0.6158 Example 9 80 19 1 0.2 0.08 60 Example 10 76 23.2 0.8 0.8 0.06 62Comp. Example 7 95 5 0 2.6 181 46 Comp. Example 8 70 30 0 3.1 26 66Comp. Example 9 80 20 0 0.1 62 62 Comp. Example 10 96 0 4 3.3 94 39Comp. Example 11 86.5 3 10.5 1.2 18 31 Comp. Example 12 78 21 1 0.4 7.247

INDUSTRIAL APPLICABILITY

[0040] As described in detail above, the electroconductive low thermalexpansion ceramic contemplated by this invention realizes a material forprecision machine components which enjoy light weight and highdimensional stability and befit use in an environment demanding highcleanliness.

1. An electroconductive low thermal expansion ceramic sintered body,comprising a β-eucryptite phase in a quantity of not less than 75% byvolume and not more than 99% by volume, wherein an absolute value ofthermal expansion coefficient thereof is not more than 1.0×10⁻⁷/K at atemperature in the range of 0° C. to 50° C., a volumetric specificresistance thereof is not more than 1.0×10⁷ Ω·cm, and a specificrigidity thereof is not less than 40 GPa/g/cm³.
 2. A ceramic sinteredbody according to claim 1, wherein a balance less said β-eucryptitephase comprises carbon or a compound containing carbon other than SiC,and TiN or SiC particles.
 3. A ceramic sintered body according to claim2, wherein a content of said carbon or said compound containing carbonother than SiC is in the range of 0.5 to 4% by volume, a content of saidTiN particles is in the range of 0.5 to 12% by volume, and a content ofsaid SiC particles is in the range of 6 to 24.5% by volume.
 4. A ceramicsintered body according to claim 1 or claim 2, wherein an averageparticle diameter of said β-eucryptite phase is in the range of 0.5 to 5μm, an average particle diameter of said TiN particles is in the rangeof 0.5 to 3 μm, and an average particle diameter of said SiC particlesis in the range of 0.2 to 3 μm.
 5. A ceramic sintered body according toany of claims 2-4, wherein a textural structure of said sintered bodyhas TiN or SiC particles dispersed discretely therein and has the carbonor the compound containing carbon other than SiC formed a grain boundaryphase in at least part of the grain boundary of said β-eucryptite phaseand/or said TiN or SiC particles.
 6. A ceramic sintered body accordingto claim 5, wherein an average thickness of said grain boundary phase inthe direction perpendicular to said grain boundary is not more than 10%of an average crystal particle diameter of said β-eucryptite.